Study of the effect of chloride ion on the ferric ion yield of the Fricke dosemeter in the absence of impurities

Significant chloride ion effects on G(Fe3+), not related to the suppression of impurity effects, have been measured for the authors' dosemeter solutions. This observation necessitates a modification of an earlier recommendation to use the absence of a Cl- effect as a purity criterion. The data reveal a cubic root relationship with the sodium chloride concentration. This relationship is shown to hold up to 1 mol 1-1Cl-, after suitable correction for the increased density of the dosemeter solution and for the effect of chloro-Fe3+ complexes at high Cl- concentration. The measured G-value decrease corresponds exactly to the decrease of the initial H2O2 yield in the presence of Cl-, i.e. it equals 2ΔGsub(H2O2): however, a suitable reaction mechanism could not be put forward. (author)